Weld

Weld (also called Dyers' Rocket) is the oldest known source of yellow dye. It has been used in Britain at least since the Viking era, and probably long before that. It produces acid yellow with alum mordant, an old gold colour with chrome, and green with iron. The dye is very fast.

Weld frequently appears when ground is disturbed and its seeds are brought to the surface, having lain dormant perhaps for hundreds of years. Frost is said to encourage germination, but in my experience light is the main factor.

It grows as a flat rosette of crinkly, dark green leaves in its first year. It makes rapid growth the following year, producing flower spikes from 3 to 5 feet high. The greatest concentration of dye is present at the beginning of flowering.

Stems, leaves and flowers can all be used for dyeing, and the whole plant may be dried and stored for later use.

Cultivation

The plant is grown from seeds, which are very small and need light to germinate. It may be grown as an annual or as a biennial. Weld prefers light, well-drained, neutral to alkaline soil, and plenty of sunlight.

The highest yield of dye is obtained when the soil is low in nitrogen. The plant makes a strong tap root and does not transplant well, so the seed should be sown in its flowering position. Prepare a fine tilth and sow shallowly or on the surface of the soil, in late summer or early spring.

Harvest and Preservation

For maximum dye content, cut the plant about 10 days after the start of flowering. All the arial parts of the plant contain dye. It can be used fresh, or dried for storage by hanging it in an airy place, away from strong light. Alternatively, the dye can be extracted and concentrated, then stored in a jar.

Dyeing

The main dye principle in Weld, luteolin, is only partially soluble in water. For this reason, the traditional method of using it was to put the chopped plant material in the dyepot along with the mordanted wool. As the wool takes up dye from solution, more dye is released from the plant. It is advisable to place the plant material in a fine-mesh bag, to avoid bits of it becoming entangled in the wool.

Simmer the wool in the dye for about 30 minutes, or until the desired shade is obtained. A small amount of alkali added to the dyebath helps the dye to dissolve. Weld contains a good proportion of dye, so about half the weight of fresh plant material to wool usually gives a good shade.